The invention arose from concerns associated with undesired oxide formation in capacitors wherein the lower capacitor plate comprises platinum and the capacitor dielectric material is barium strontium titanate. A typical prior art construction is shown in FIG. 1, and includes a semiconductor wafer fragment indicated generally by reference numeral 10. Such comprises a bulk substrate 12 having associated source/drain areas 14 provided therewithin and a patterned electrically conductive word line 16 formed thereatop. An electrically insulating borophosphosilicate glass (BPSG) layer 18 is provided over substrate 12 and word line 16. A contact opening 20 is provided to extend downwardly to one of source/drain regions 14 for providing electrical connection relative to a capacitor. Contact opening 20 is filled with conductively doped polysilicon to form a plug 22.
A lower capacitor plate which makes electrical connection with polysilicon plug 22 is indicated with reference numeral 24, and preferably comprises Pt. It is desirable that the platinum of bottom storage node 24 not interface or interdiffuse with the silicon of plug 22. To prevent such diffusion and reaction, an electrically conductive reaction barrier layer 26, typically TiN is interposed between silicon plug 22 and platinum storage node 24. Subsequently, a thin capacitor dielectric layer 28 is provided over lower capacitor plate 24, followed by a final cell capacitor plate layer 30. An increasingly popular and desired material for capacitor dielectric layer 28 is barium strontium titanate.
The illustrated FIG. 1 construction is the desired ideal, although such does not practically occur during processing. Specifically and with reference to FIG. 2, the provision of TiN layer 26 in combination with a titanate layer such as barium strontium titanate, subjects layer 26 to undesired oxidation. Such results in formation of a wedge-shaped oxide layer 32 resulting from reaction of TiN to form titanium oxide. This actually causes platinum of storage node 26 to rise or wedge upwardly as shown. Such creates stresses and cracking as well as undesirably creating greater varying vertical topography.
It would be desirable to overcome such prior art problems in capacitor constructions.